A few other primates have the word "ape" in their common names, but they are not regarded as true apes by most authorities.

Except for gorillas and humans, all true apes are agile climbers of trees. They are best described as omnivorous, their diet consisting of fruit, grass seeds, and in most cases some quantities of meat and invertebrates—either hunted or scavenged—along with anything else available and easily digested. They are native to Africa and Asia, although humans have spread to all parts of the world.

Most ape species are rare or endangered. The chief threat to most of the endangered species is loss of tropical rainforest habitat, though some populations are further imperiled by hunting for bushmeat.

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"Ape" (Old Eng. apa; Dutch aap; Old Ger. affo; Welsh epa; Old Czech op) is a word of uncertain origin and is possibly an onomatopoetic imitation of animal chatter. The term has a history of rather imprecise usage. Its earliest meaning was a tailless (and therefore exceptionally human-like) non-human primate, but as zoological knowledge developed it became clear that taillessness occurred in a number of different and otherwise unrelated species.

Until a handful of decades ago, humans were thought to be distinctly set apart from the other apes (even from the other great apes), so much so that many people still don't think of the term "apes" to include humans at all. However, it is not considered accurate by many biologists to think of apes in a biological sense without considering humans to be included [How to reference and link to summary or text]. The terms "non-human apes" or "non-human great apes" is used with increasing frequency to show the relationship of humans to the other apes while yet talking only about the non-human species [How to reference and link to summary or text].

The gibbon family, Hylobatidae, is composed of thirteen medium-sized species. Their major distinction are their long arms which they use to brachiate through the trees. As an evolutionary adaptation to this arboreal lifestyle, their wrists are ball and socket joints. The largest of the gibbons, the Siamang, weighs up to 23 kg (50 lb). In comparison, the smallest great ape is the Common Chimpanzee at a modest 40 to 65 kg (88 to 143 lb).

The great ape family was previously referred to as Pongidae, and humans (and fossil hominids) were omitted from it, but there is no biological case for doing this. However, this definition is still used by many anthropologists and by lay people. However, that definition makes Pongidae paraphyletic, whereas most taxonomists nowadays encourage monophyletic groups, even though there might not be much signifigance. Chimpanzees, gorillas, humans and orangutans are all more closely related to one another than any of these four genera are to the gibbons. However, the term "hominid" is still used with the specific meaning of extinct animals more closely related to humans than the other great apes (for example, australopithecines). It is now usual to use even finer divisions, such as subfamilies and tribes to distinguish which hominoids are being discussed. Current evidence implies that humans share a common, extinct, ancestor with the chimpanzee line, from which we separated more recently than the gorilla line.

Both great apes and lesser apes fall within Catarrhini, which also includes the Old World monkeys of Africa and Eurasia. Within this group, both families of apes can be distinguished from these monkeys by the number of cusps on their molars (apes have five—the "Y-5" molar pattern, Old World monkeys have only four in a "bilophodont" pattern). Apes have more mobile shoulder joints and arms, ribcages that are flatter front-to-back, and a shorter, less mobile spine compared to Old World monkeys. These are all anatomical adaptations to vertical hanging and swinging locomotion (brachiation) in the apes. All living members of the Hylobatidae and Hominidae are tailless, and humans can therefore accurately be referred to as bipedal apes. However, there are also primates in other families that lack tails, and at least one (the Pig-Tailed Langur) that has been known to walk significant distances bipedally.

Although the hominoid fossil record is far from complete, and the evidence is often fragmentary, there is enough to give a good outline of the evolutionary history of humans. The time of the split between humans and living apes used to be thought to have occurred 15 to 20 million years ago, or even up to 30 or 40 million years ago. Some apes occurring within that time period, such as Ramapithecus, used to be considered as hominins, and possible ancestors of humans. Later fossil finds indicated that Ramapithecus was more closely related to the orangutan, and new biochemical evidence indicated that the last common ancestor of humans and other hominins occurred between 5 and 10 million years ago, and probably in the lower end of that range.

The intelligence and humanoid appearance of apes are responsible for legends which attribute human qualities; for example, they are sometimes said to be able to speak but refuse to do so in order to avoid work.

They are also said to be the result of a curse—a Jewishfolktale claims that one of the races who built the Tower of Babel became apes as punishment, while Muslim lore says that the Jews of Elath became apes as punishment for fishing on the Sabbath. Some sects of Christian have folklore that claims that apes are a symbol of lust and were created by Satan in response to God's creation of humans. It is uncertain whether any of these references are to any specific apes, since all date from a period when the distinction between apes and monkeys was not widely understood, or not understood at all.

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Humans and the other apes share many similarities, including the ability to properly use tools and imitate others. Recent studies at Yale test some of these similarities. A professor and his/her students gave a challenge to baby humans and baby chimps. Both groups were shown a way that might solve this challenge. However, neither group knew that the solution they were shown was incorrect. Both times the baby humans tried to complete the challenge, they imitated what they were shown and failed at the attempt. The chimpanzee babies also failed their first attempt, as they too mimiced what they were shown. However, on their second attempt, they created a novel solution, and thus completed the challenge. The professor interpreted this as meaning that baby chimps learn from experience, while baby humans just imitate what they are shown. This gave scientists key information in understanding the cultural aspects of ape life and evolutionary similarities between humans and apes.

There have also been recent breakthroughs in evidence of ape culture that go beyond what was explained above. This was further explored by scientists at the convention in St. Louis.[3]

The history of hominoid taxonomy is somewhat confusing and complex. The names of subgroups have changed their meaning over time as new evidence from fossil discoveries, anatomy comparisons and DNA sequences, has changed understanding of the relationships between hominoids. The story of the hominoid taxonomy is one of gradual demotion of humans from a special position in the taxonomy to being one branch among many. It also illustrates the growing influence of cladistics (the science of classifying living things by strict descent) on taxonomy.

In 1758, Carolus Linnaeus, relying on second- or third-hand accounts, placed a second species in Homo along with H. sapiens: Homo troglodytes ("cave-dwelling man"). It is not clear to which animal this name refers, as Linnaeus had no specimen to refer to, hence no precise description. Linnaeus named the orangutan Simia satyrus ("satyr monkey"). He placed the three genera Homo, Simia and Lemur in the family of Primates.

The troglodytes name was used for the chimpanzee by Blumenbach in 1775 but moved to the genus Simia. The orangutan was moved to the genus Pongo in 1799 by Lacépède.

Linnaeus's inclusion of humans in the primates with monkeys and apes was troubling for people who denied a close relationship between humans and the rest of the animal kingdom. Linneaus's Lutheran Archbishop had accused him of "impiety." In a letter to Johann Georg Gmelin dated February 25, 1747, Linnaeus wrote:

It is not pleasing to me that I must place humans among the primates, but man is intimately familiar with himself. Let's not quibble over words. It will be the same to me whatever name is applied. But I desperately seek from you and from the whole world a general difference between men and simians from the principles of Natural History. I certainly know of none. If only someone might tell me one! If I called man a simian or vice versa I would bring together all the theologians against me. Perhaps I ought to, in accordance with the law of Natural History.[5]

Accordingly, Johann Friedrich Blumenbach in the first edition of his Manual of Natural History (1779), proposed that the primates be divided into the Quadrumana (four-handed, i.e. apes and monkeys) and Bimana (two-handed, ie. humans). This distinction was taken up by other naturalists, most notably Georges Cuvier. Some elevated the distinction to the level of order.

However, the many affinities between humans and other primates — and especially the great apes — made it clear that the distinction made no scientific sense. Charles Darwin wrote, in The Descent of Man:

The greater number of naturalists who have taken into consideration the whole structure of man, including his mental faculties, have followed Blumenbach and Cuvier, and have placed man in a separate Order, under the title of the Bimana, and therefore on an equality with the orders of the Quadrumana, Carnivora, etc. Recently many of our best naturalists have recurred to the view first propounded by Linnaeus, so remarkable for his sagacity, and have placed man in the same Order with the Quadrumana, under the title of the Primates. The justice of this conclusion will be admitted: for in the first place, we must bear in mind the comparative insignificance for classification of the great development of the brain in man, and that the strongly-marked differences between the skulls of man and the Quadrumana (lately insisted upon by Bischoff, Aeby, and others) apparently follow from their differently developed brains. In the second place, we must remember that nearly all the other and more important differences between man and the Quadrumana are manifestly adaptive in their nature, and relate chiefly to the erect position of man; such as the structure of his hand, foot, and pelvis, the curvature of his spine, and the position of his head.[6]

Until about 1960, the hominoids were usually divided into two families: humans and their extinct relatives in Hominidae, the other apes in Pongidae.[7]

The 1960s saw the application of techniques from molecular biology to primate taxonomy. Goodman used his 1963 immunological study of serum proteins to propose a division of the hominoids into three families, with the non-human great apes in Pongidae and the lesser apes (gibbons) in Hylobatidae.[8] The trichotomy of hominoid families, however, prompted scientists to ask which family speciated first from the common hominoid ancestor.

Within the superfamily Hominoidea, gibbons are the outgroup: this means that the rest of the hominoids are more closely related to each other than any of them are to gibbons. This led to the placing of the other great apes into the family Hominidae along with humans, by demoting the Pongidae to a subfamily; the Hominidae family now contained the subfamilies Homininae and Ponginae. Again, the three-way split in Ponginae led scientists to ask which of the three genera is least related to the others.

Investigation showed orangutans to be the outgroup, but comparing humans to all three other hominid genera showed that African apes (chimpanzees and gorillas) and humans are more closely related to each other than any of them are to orangutans. This led to the placing of the African apes in the subfamily Homininae, forming another three-way split. This classification was first proposed by M. Goodman in 1974.[9]

To try to resolve the hominine trichotomy, some authors proposed the division of the subfamily Homininae into the tribes Gorillini (African apes) and Hominini (humans).

However, DNA comparisons provide convincing evidence that within the subfamily Homininae, gorillas are the outgroup. This suggests that chimpanzees should be in Hominini along with humans. This classification was first proposed (though one rank lower) by M. Goodman et. al. in 1990.[2] See Human evolutionary genetics for more information on the speciation of humans and great apes.

As discussed above, hominoid taxonomy has undergone several changes. Current understanding is that the apes diverged from the Old World monkeys about 25 million years ago. The lesser and greater apes split about 18 mya, and the hominid splits happen 14 mya (Pongo), 7 mya (Gorilla), and 3-5 mya (Homo & Pan)